we begin with the worldwide reaction today to a dangerous move in syria. chemicals, dead lly gas loaded onto weapons near an airfield there. one drop could kill within minutes. so, world leaders are mobilizing tonight, deciding what they're going to do. and abc's senior foreign affairs correspondent martha raddatz takes us inside that story. >> reporter: today, hillary clinton, overseas, trying to tind some dip mroep matic way to end this increasingly dangerous conflict. 20 months of fighting, 40,000 lives lost. and now the chilling possibility of an air attack with deadly nerve agents. >> there is no question that we remain very concerned that the regime might very well consider the use of chemical weapons. >> reporter: a senior u.s. official saying that over the weekend, the syrian military loaded components of the nerve gas sarin into bombs on or near syrian airfields. they have not loaded the bombs onto aircraft, but the threat remains. >> once these chemicals are poured into weapons, artillery shells, bombs that can be dropped from airplanes, they can